Membrane vacuum pump

ABSTRACT

A membrane vacuum pump includes at least one membrane pump stage, at least one inlet valve for a process gas to be conveyed associated with the membrane pump stage, and at least one gas ballast valve for the supply of a ballast gas. The flow path for the ballast gas, leading through the gas ballast valve, opens into the flow path for the process gas behind the inlet valve in the direction of flow of the process gas.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a membrane vacuum pump having at least one membrane pump stage.

2. Description of the Prior Art

Membrane vacuum pumps are suitable for evacuating gas volumes and can, in dependence on the application, be directly connected to a volume to be evacuated or can serve as a roughing pump for a further vacuum pump which is connected upstream of the membrane vacuum pump in the direction of flow, for example for a turbomolecular pump. To provide a desired performance behavior, the membrane vacuum pump can comprise one or more membrane pump stages which can be connected behind one another or in parallel with one another in the direction of flow so that the membrane pump stages can pump serially or in parallel with one another.

The condensation of water vapor in the pump space (suction space) of the vacuum pump is problematic with known membrane vacuum pumps since condensate present in the pump space impairs the functional safety of the vacuum pump and reduces its service life.

To reduce the influence of the condensation of liquids on the functional safety and service life of the membrane vacuum pump, a ballast gas device can be used to conduct a ballast gas (gas ballast) into the pump space of the vacuum pump. In this respect, the ballast gas serves to prevent the formation of condensate and to remove existing condensate from the pump space. With known ballast gas devices, the condensate formation can, however, not be reliably prevented at all times everywhere in the pump space and the quantity of the ballast gas which can be supplied is limited. Furthermore, on the use of known ballast gas devices, the final vacuum pressure which can be reached with the vacuum pump is increased.

In addition, known ballast devices substantially increase the construction space required for the realization of the vacuum pump and do not allow an automatic time control of the ballast gas supply.

It is therefore the object of the invention to provide a membrane vacuum pump which overcomes the above-described disadvantages and in which in particular condensate formation is completely and reliably prevented at all times without the pump properties of the vacuum pump thereby being degraded.

SUMMARY OF THE INVENTION

The object of the invention is achieved by a membrane vacuum pump that comprises at least one membrane pump stage, at least one inlet valve for a process gas to be conveyed associated with the membrane pump stage and at least one gas ballast valve for supplying a ballast gas. The flow path for the ballast gas leading through the gas ballast valve opens into the flow path for the process gas behind the inlet valve in the direction of flow of the process gas.

Since the ballast gas path opens into the process gas path behind the inlet valve in the direction of flow of the process gas, the inlet valve prevents the ballast gas from flowing in the direction opposite to the process gas flow to the pump inlet of the membrane vacuum pump and thereby increases the final vacuum pressure of the pump which can be achieved. At the same time, the ballast gas can reach the total pump space of the membrane vacuum pump so that a complete purging of the pump space is achieved and condensation formation is effectively prevented everywhere. A degrading of the pump properties and in particular of the achievable final pressure is even avoided on the supply of a high ballast gas quantity which reliably and completely prevents condensate formation.

Advantageous embodiments of the invention are set forth in the dependent claims, in the description and in the FIGURE.

In accordance with an advantageous embodiment, the flow path for the ballast gas opens into the flow path for the process gas directly behind the inlet valve. It is thereby ensured that the total pump space of the vacuum pump is purged with the supplied ballast gas and condensate formation is effectively avoided everywhere in the pump space.

The flow path for the ballast gas can open into the flow path for the process gas, for example, in a connection region or connection passage arranged between the inlet valve and the suction space of the membrane pump stage so that this region can also be purged with the ballast gas. The suction space of the membrane pump stage can be bounded in a manner known per se by a static head cover and by a movable membrane. The connection region or connection passage between the inlet valve and the suction space can in this case be bounded fully or in part by the head cover.

The flow path for the ballast gas can also open directly into the suction space in the direct vicinity of the connection passage for the process gas or the flow path for the ballast gas and the flow path for the process gas can meet in the region of a common opening of the suction space.

The flow path for the ballast gas can lead through a ballast gas passage which is preferably bounded at least partly and in particular fully by the head cover of the membrane pump stage.

The valve is preferably a valve which can be electrically actuated. In accordance with an advantageous embodiment, the gas ballast valve is an electromagnetic valve. Such a valve can be realized in a small construction space and can be electrically controlled so that an automatic actuation of the valve can take place.

A control device, in particular a digital control device, is preferably provided which is operationally connected to the gas ballast valve and with which the gas ballast valve can be controlled, in particular electrically, for actuation, e.g. to achieve a time control of the valve actuation. The gas ballast valve is preferably automatically controllable so that the actuation of the gas ballast valve takes place in a predefined dependence on the pump operation of the vacuum pump, for example in order to avoid condensate formation as fully as possible at all times. For example, a predefined purge cycle in which the pump space is purged with the ballast gas can be carried out automatically in each case at the start of a pump cycle of the vacuum pump. The purge cycle can be followed by a performance cycle in which no ballast gas is supplied.

The control device can be adapted to actuate the gas ballast valve in dependence on measured signals which are provided by sensors of the vacuum pump and/or by external sensors and which are dependent on measurement parameters which relate to the operation of the vacuum pump or to the process to be carried out in the vacuum to be generated.

The control unit can be programmable so that a desired automatic actuation of the gas ballast valve can be individually preset by a user, e.g. in the form of settable purge cycles.

The vacuum pump can comprise at least one further membrane pump stage in addition to the one membrane pump stage. In accordance with an advantageous embodiment, the further membrane pump stage of the one membrane pump stage is connected downstream in the direction of flow of the process gas so that the ballast gas is first conveyed through the one pump stage and then through the further pump stage connected downstream. In this embodiment, the ballast gas supplied to the suction space of the first membrane pump stage automatically also reaches the further pump stage connected downstream as a result of the pump action of the vacuum pump so that both pump stages are purged and are thereby protected from condensate formation.

The membrane pump stage can also comprise more than two membrane stages, in particular three, four or more than four membrane stages, in total. It is preferred in this case if the gas ballast valve is associated with a pump stage which is arranged at the start of the membrane vacuum pump viewed in the direction of flow of the process gas, that is which follows on from the pump inlet of the membrane vacuum pump without the interposition of further pump stages. The further membrane pump stages can be connected downstream of the pump stage associated with the gas ballast valve in the direction of flow of the process gas so that the ballast gas supplied to the first pump stage is also conveyed through the further pump stages and purges them in the operation of the vacuum pump.

The flow quantity of ballast gas which can be supplied to the pump via the gas ballast valve is dependent on the flow conductivity of the gas ballast valve. A gas ballast valve having a corresponding flow conductivity can therefore simply be used to realize a desired flow quantity. Additional baffles of the vacuum pump for realizing a desired flow quantity can be dispensed with.

In accordance with an advantageous embodiment, the gas ballast valve has an adjustable conductivity. In this case, the flow quantity of the ballast gas which can be supplied to the pump can be set simply by setting the conductivity to a desired value.

As a consequence of the introduction of the ballast gas behind the inlet valve in the direction of flow of the process gas, work can be carried out with a high ballast gas quantity which ensures a reliable purging of the total pump space without degrading the performance properties of the pump For example, the ballast gas flow quantity which can be supplied via the ballast gas valve can be set so that it amounts to more than 10%, preferably more than 20%, and particularly preferably more than 30%, of the suction capability of the vacuum pump in the presence of the achievable final pressure at the pump inlet of the membrane vacuum pump and without any other gas load.

It is preferred in principle if the gas ballast valve has at least two switch positions, with the ballast gas being able to be supplied to the pump space of the vacuum pump in the one switch position of the gas ballast valve and with the gas ballast valve forming a gas-tight closure for the pump space in the other switch position.

The gas ballast valve is preferably a 3/2 way valve. The gas ballast valve accordingly preferably has two inlets as well as one outlet which is selectively connectable to one of the two inlets in a gas-conductive manner by switching over the gas ballast valve. The outlet of the gas ballast valve is preferably connected in a gas-conductive manner to the pump space of the pump, while a ballast gas can preferably be supplied to one of the inlets and the other inlet is preferably sealed in a gas-tight manner. In the one switch position, the ballast gas can consequently be supplied to the pump space, whereas the gas ballast valve forms a gas-tight closure for the pump space in the other switch position.

The inlet valve of the membrane pump stage and/or an outlet valve of the membrane pump stage can be configured such that it only passes a gas flow through in the desired direction of flow of the process gas and prevents a return gas flow. The inlet valve and/or an outlet valve of the membrane pump stage can, for example, be configured as a gas flow-controlled valve, for example as a gas flow-controlled flutter valve. A backflow of the ballast gas against the direction of flow of the process gas is consequently avoided by the supply of the ballast gas behind the inlet valve in the direction of flow.

In accordance with an advantageous embodiment, a filter, in particular a fine filter, is provided for filtering the ballast gas. The filter is preferably arranged in front of the opening of the flow path of the ballast gas into the flow path of the process gas in the direction of flow of the ballast gas. The filter can be arranged in front of the gas ballast valve in the direction of flow of the ballast gas. The gas ballast valve and the pump space of the vacuum pump are thereby protected from contaminants from the outside.

A further embodiment provides that a drive unit of the vacuum pump and the gas ballast valve can be actuated with an electrical voltage of the same value, such as 24 volts, for example. Accordingly, a common power supply unit can be provided for the provision of a power supply for the drive unit and for the gas ballast valve. The effort required for manufacturing the vacuum pump is thereby reduced.

A further subject of the invention is a pump arrangement having at least one membrane vacuum pump in accordance with the present description and having at least one further vacuum pump connected to the membrane vacuum pump in series in a gas-conductive manner upstream of the membrane vacuum pump. The further vacuum pump can, for example, be a turbomolecular pump, a single-stage or multi-stage Roots pump, a rotary vane pump, a scroll pump, a claw pump, a screw pump, a rotary piston pump, or an ion getter pump.

The membrane vacuum pump preferably serves as a roughing pump for the further vacuum pump connected upstream. Condensate formation in the membrane vacuum pump is prevented by the gas ballast valve so that the operating security, the reliability and the operating service life of the membrane vacuum pump are increased without the roughing pressure which can be provided for the further vacuum pump by the membrane vacuum pump thereby being increased.

The invention will be described by way of example in the following with reference to an advantageous embodiment and to the enclosed FIGURE.

BRIEF DESCRIPTION OF THE DRAWINGS

Single FIGURE of the drawings shows a cross-sectional view of a membrane vacuum pump in accordance with an embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The membrane vacuum pump shown in FIG. 1 comprises a first membrane pump stage 12 and a second membrane pump stage 14 which are connected behind one another in the direction of flow and which pump in series. The first pump stage 12 comprises an inlet 18 which simultaneously forms the pump inlet of the pump. A supply line 60 for the process gas to be conveyed is connected to the inlet 18. The supply line 60 can connect the membrane vacuum pump to the outlet side of a turbomolecular pump connected upstream, for example, so that the membrane vacuum pump serves as a roughing pump for the turbomolecular pump.

An inlet passage 24 formed in the housing 16 of the pump leads from the inlet 18 to an inlet valve 20 of the pump stage 12. The inlet valve 20 is configured as a gas flow-controlled valve having a valve platelet 64 and only allows a gas flow in the direction of flow of the process gas marked by the arrows 56 in FIG. 1. The inlet valve 20 is preferably arranged between a housing cover of the housing 16 bounding the inlet passage 24 and a head cover of the housing 16 bounding the suction space 30 of the pump stage 12 and not shown as a separate part in FIG. 1 for reasons of simplicity.

A connection passage 26 which connects the outlet side of the inlet valve 20 in a gas-conductive manner to the suction space 30 of the pump stage 12 is arranged at the outlet side of the inlet valve 20 and extends through the head cover. The suction space 30 is bounded by the head cover and by a membrane 32 which is supported via a connecting rod 34 at a rotatingly drivable crankshaft 35.

The pump shown in FIG. 1 additionally comprises a gas ballast valve 22 which is supplied with a ballast gas via a supply line 62. The gas ballast valve 22 is configured as a 3/2 way valve and comprises one outlet and two outlets. The outlet of the gas ballast valve 22 is connected in a gas-conductive manner to a ballast gas passage 28 which is bounded by the head cover of the pump stage 12 and which opens into the connection passage 26.

One of the inlets of the gas ballast valve 22 is connected to the supply line 62 for the ballast gas so that the supply line 62 is interconnected in the corresponding switch position of the gas ballast valve 22 and the ballast gas is conveyed in accordance with the arrow 58 into the ballast gas passage 28 and from there via the connection passage 26 into the suction space 30. The other inlet of the gas ballast valve 22 is sealed in a gas-tight manner so that the gas ballast valve 22 forms a gas-tight closure for the pump space in the corresponding switch position which is shown in FIG. 1.

The gas ballast valve 22 is configured as an electromagnetic valve and is preferably connected to an electronic control unit which is not shown in FIG. 1 and which automatically controls the gas ballast valve 22. The gas ballast valve 22 is shown in the schematic representation of FIG. 1 within a separate supply line 62 for the ballast gas. The gas ballast valve 22 can be fixedly connected to the housing 16 of the membrane vacuum pump in practice, in particular to the housing cover or to the head cover of the first pump stage 12 and can in particular be integrated into the housing 16. The gas ballast valve 22 can, for example, be directly connected to the housing 16 at the inlet of the ballast gas passage 28 and/or the gas ballast valve 22 can be arranged fully or partly within the ballast gas passage 28.

The pump stage 12 furthermore comprises a gas flow-controlled outlet valve 36 which is connected in a gas-conductive manner to the suction space 30 via a connection passage arranged in the head cover and which is configured only to pass the conveyed gas through in the direction of flow 56 directed away from the suction space 30. The outlet valve 36 is connected to an outlet 38 of the pump stage 12 at the outlet side.

A connection line 40 connects the outlet 38 of the first pump stage 12 to the inlet 42 of the second pump stage 14 so that the pump stage 12, 14 are connected behind one another in the direction of flow 56 and pump in series with one another. It is in principle also possible to connect the two pump stages in parallel with one another so that they pump in parallel with one another. It is possible for this purpose to connect the respective inlets of both pumps to the pump inlet of the vacuum pump and to connect the respective outlets of both pump stages to the pump outlet of the vacuum pump.

The second pump stage 14 is configured substantially identically with the first pump stage 12. A gas flow-controlled inlet valve 44 having a valve platelet 68 which connects the inlet 42 to the suction space 46 of the second pump stage 14 follows on from the inlet 42 of the second pump stage 14. The suction space 44 is bounded, as described above with respect to the first pump stage 12, by a head cover of the housing 16 not shown as a separate part in FIG. 1 and by a membrane 48 which is coupled via a connecting rod 50 to the rotatingly drivable crankshaft 35. The second pump stage 14 comprises an outlet valve 52 having a valve platelet 70 via which the gas expelled from the suction space 46 can be supplied to an outlet 54 of the second pump stage 14, said outlet simultaneously forming the pump outlet of the membrane vacuum pump.

The operation of the vacuum pump shown in FIG. 1 is explained in the following.

In the operation of the vacuum pump, the crankshaft 35 is rotatingly driven so that the connecting rods 34, 50 are moved cyclically up and down with the membranes 32, 48 of the two pump stages 12, 14 fastened thereto. A cycle comprises for each pump stage 12, 14 a suction phase in which the gas to be conveyed is sucked via the respective inlet valve 20, 44 into the suction space 30, 46 and a subsequent expulsion phase in which the gas to be conveyed is expelled via the respective outlet valve 36, 52 out of the suction space 30, 46 and is pumped therethrough. A serial pump operation in which the gas to be conveyed which is applied at the inlet 18 is first pumped via the first pump in the direction of the arrows 56 and is subsequently pumped via the second pump stage to the outlet 54 is ensured by the connection line 40.

In the final phase of a pump cycle, the gas ballast valve 22 is respectively located in the switch position shown in FIG. 1. In this position of the gas ballast valve 22, the gas ballast valve 22 forms a gas-tight closure for the pump space so that no ballast gas moves into the pump space.

To avoid any formation of condensate in the pump space of the vacuum pump and to remove any condensate which is present, a purge cycle is carried out regularly, in particular at the start of each pump cycle of the pump, during which purge cycle the gas ballast valve 22 is located in the second switch position.

In the second switch position of the gas ballast valve 22, the supply line 62 for the ballast gas is throughgoing so that the pump stages 12, 14 convey the ballast gas via the ballast gas passage 28 into the pump space of the membrane vacuum pump in addition to the gas to be conveyed applied at the inlet 18. The flow path of the ballast gas opens in the region of the connection passage 26 and consequently into the flow path of the process gas directly behind the inlet valve 20 in the direction of flow of the process gas. The total pump space of the pump stages 12, 14 arranged behind the inlet valve 12, 14 is consequently purged by the ballast gas so that condensate formation is effectively avoided everywhere. 

What is claimed is:
 1. A membrane vacuum pump comprising at least one membrane pump stage (12), at least one inlet valve (20) for a process gas to be conveyed and at least one gas ballast valve (22) for the supply of a ballast gas, wherein the at least one inlet valve (20) is associated with the membrane pump stage (12), and wherein the flow path for the ballast gas leading through the gas ballast valve (22) opens into the flow path for the process gas behind the inlet valve (20) in the direction of flow of the process gas.
 2. The vacuum pump in accordance with claim 1, wherein the flow path for the ballast gas opens into the flow path for the process gas directly behind the inlet valve (20).
 3. The vacuum pump in accordance with claim 1, wherein the gas ballast valve (22) is an electromagnetic valve.
 4. The vacuum pump in accordance with claim 1, further comprising a control device, the control device being operationally connected to the gas ballast valve (22) and the gas ballast valve (22) being able to be controlled for actuation by the control device.
 5. The vacuum pump in accordance with claim 1, further comprising at least one further membrane pump stage (14) in addition to the one membrane stage (12).
 6. The vacuum pump in accordance with claim 5, wherein the at least one further membrane pump stage (14) is connected downstream of the one membrane pump stage (12) in the direction of flow of the process gas.
 7. The vacuum pump in accordance with claim 1, wherein the gas ballast valve (22) has an adjustable connectivity.
 8. The vacuum pump in accordance with claim 1, wherein the gas ballast valve (22) is a 3/2 way valve.
 9. The vacuum pump in accordance with claim 1, further comprising a filter for filtering the ballast gas.
 10. The vacuum pump in accordance with claim 9, wherein the filter is arranged in front of the opening of the flow path of the ballast gas into the flow path of the process gas in the direction of flow of the ballast gas.
 11. The vacuum pump in accordance with claim 1, wherein a drive unit of the vacuum pump and the gas ballast valve (22) can be actuated with an electrical voltage of the same value.
 12. The vacuum pump in accordance with claim 1, further comprising a common power supply unit for the provision of a power supply for the drive unit and for the gas ballast valve (22).
 13. A pump arrangement having at least one membrane vacuum pump comprising at least one membrane pump stage (12), at least one inlet valve (20) for a process gas to be conveyed and at least one gas ballast valve (22) for the supply of a ballast gas, wherein the at least one inlet valve (20) is associated with the membrane pump stage (12), and wherein the flow path for the ballast gas leading through the gas ballast valve (22) opens into the flow path for the process gas behind the inlet valve (20) in the direction of flow of the process gas; and having a further vacuum pump connected in a gas-conductive manner in series to the membrane vacuum pump upstream of the membrane vacuum pump.
 14. The pump arrangement in accordance with claim 13, wherein the further vacuum pump is selected from the group of members comprising a turbomolecular pump, a single-stage or multi-stage Roots pump, a rotary vane pump, a scroll pump, a claw pump, a screw pump, a rotary piston pump and an ion getter pump. 